DESCRIPTION: The investigator has established that CNS-derived neural cell lines are excellent in vitro models of CNS neurons and that the neonatal and adult CNS can direct precise differentiation of transplanted neural precursors. The present proposal will build on these observations by addressing 5 specific questions. 1. Do transplanted RN33B cells functionally integrate into the host CNS? Cells transplanted into the hippocampus will be examined for the extent and course of axonal projections. The electrophysiological properties of these cells will be determined in slice preparations and the behavioral consequences of transplantation of these cells into the hippocampus depleted of CA1 pyramidal cells will be examined under these different conditions. 2. What are the potential mechanisms that control RN33B and RN46A cell survival and differentiation in vivo? The role of neurotrophic factors in mediating cell differentiation will be defined by engineering cells to secrete specific neurotrophic factors or their receptors and then transplanting cells into different CNS regions. Cell survival and morphological differentiation will be examined 3. What are the molecular mechanisms that determine neurotransmitter phenotype in RN46A cells? Signaling pathways in RN46A cells lead to specific cell differentiation. The investigator will describe transcriptional control of tryptophan hydroxylase (TPH) mRNA synthesis by BDNF and CNTF and then will examine post-translational mechanisms through which BDNF activates TPH. 4. Define the optimal neural cell type for motor neuron replacement using a sciatic nerve lesion in neonatal rats to deplete the motor neuron pool. The potential to replace lost motor neurons with phenotypically correct cells will be examined, using primary cell isolates, hybrid cell lines or genetically engineered cells. 5. Do fetal human brainstem stem cells and neural cell lines have similar potential for transplantation? This will be a direct extension of the rodent cell line work and will determine whether similar molecular mechanisms control their differentiation in vitro and after transplantation into appropriate animal models.